Conventionally, work vehicles such as a hydraulic excavator have been known. For example, Japanese Utility Model Laying-Open No. 04-26263 (PTD 1) discloses a power excavator configured to have an actuator that is supplied with pressurized oil discharged from a hydraulic pump to drive a boom, an arm and a bucket via a work implement hydraulic circuit, thereby operating the boom, the arm and the bucket.
Specifically, the power excavator in PTD 1 has a heavy lifting (power-up) function. Specifically, the power excavator includes: a variable-type relief valve configured to variably set the pressure inside the work implement hydraulic circuit at two levels including a high level and a low level; detection means for detecting each of the operation states of the boom, the arm and the bucket; and means for variably-operating the variable-type relief valve. The means for variably-operating the variable-type relief valve is configured to variably-operate the variable-type relief valve so as to set the pressure inside the work implement hydraulic circuit at a high pressure at the time when the detecting means detects that the arm and the bucket each are fixed at a fixed position and that the boom is raised.
Thus, according to the power excavator in PTD 1, power-up is implemented on the conditions that “the arm and the bucket each are fixed at a fixed position” and “the boom is operated”.